For performance, I agree with many here, it's not the number one priority. The critical parts missing are: (1) a way to install web apps that hasn't to be lear

For performance, I agree with many here, it's not the number one priority. The critical parts missing are: (1) a way to install web apps that hasn't to be learned, like Mozilla's Intall API, and unlike the bookmark to homescreen UI (2) offline APIs: ServiceWorkers seem great but, Safari support could come as late as fall 2016 I guess, and be botched up for a year or two like they did with the history API and IndexedDB; in the meantime, offline web apps are screwed (3) full screen API: not having the ugly address bar all the time which reminds users this app is unlike others and may be substandard; and being able to lock screen orientation (4) notification API: the users expect anything important your app displays, they can be notified about, otherwise, your app seems unreliable Except, the notification API, both iOS and Android had all of those from the start. Only then should we worry about performance, sensors, frameworks, layouts, ... Regarding image decoding, why can't browser vendors do it today off the main thread? Is a change in web standards required? It seems no one has implemented it, so if it was a low-hanging fruit material to performance, it would be done already. In my experience, image decoding is only an issue for infinite scrolling, when javascript inserts images too late for the browser to have smooth scrolling. Infinite scrolling is nice sometimes but not all lists have to be infinite, have they?